Extreme Networks Alpine 3804 Hardware Manual page 270

BlackDiamond 6800 Series I/O Modules
QoS and Differentiated Services. The ATM module supports eight ingress queues and eight egress
queues per port. The scheduling parameters for these queues (minimum bandwidth, maximum
bandwidth, priority level, etc.) are controlled by QoS profiles that you can customize for individual
ingress or egress queues on a specific ATM port.
You can assign frames to queues based on IEEE 802.1p priorities, Differentiated Services Code Points
(DSCPs), or by configuring a QoS profile for the port or VLAN. You can tailor the DSCP-to-queue
mapping on a per-port basis. Most of the existing ingress classification functions, along with the
DiffServ replacement functions, are also supported for ATM ports.
The supported DiffServ functions maximize user flexibility while providing all of the features needed to
support the standard per-hop behaviors (PHBs), including:
• Default
• Class Selector
• Assured Forwarding
• Expedited Forwarding
The ATM module also provides flexible support for the well-known Weighted RED (WRED) congestion
avoidance algorithm.
Service Provider Features
The ATM module provides the following features for service provider environments:
• DSCP mapping
• VLAN ID (VID) tag mapping
• VLAN ID (VID) tag nesting
• VLAN to PVC mapping
DSCP Mapping. You can use the command to configure a mapped
diffserv dscp-mapping
relationship between an input DSCP and an associated output DSCP. Each ATM port supports three
DSCP mapping tables: one of the tables is used in the ingress direction; two are used for egress flows
(onto the ATM link). The two egress tables are for the congested and noncongested states, as
determined by the RED algorithm. If RED is not enabled on the ATM port, the egress congested-state
mapping table is not used.
In the ingress direction, the input DSCP of a packet received from the ATM link is replaced by an
output DSCP before the packet is forwarded. In the egress direction, the operation is similar, except that
the DSCP mapping occurs before the packet is transmitted onto the ATM link.
One potential use of the DSCP mapping capability is to reconcile varying DiffServ policies at the
boundary between autonomous systems, such as at the boundary between two ISPs. The availability of
different tables for the congested and noncongested states is useful in marking operations that increase
the probability of packets being dropped during times of congestion, as discussed in the DiffServ
Assured Forwarding RFC (RFC 2597).
VLAN ID (VID) Tag Mapping. An analogous feature has been added for the managing of 802.1Q tags.
The command provides support for VLAN ID (VID) mapping tables. Each ATM
dot1q tagmapping
port supports two VID tables: one table is used in the ingress direction; the other is used in the egress
direction. Each of the tables enables an input VID to be mapped to an output VID. This feature is useful
in reconciling policy differences at the boundary between the customer and the service provider.
270 Extreme Networks Consolidated Hardware Guide